DNS failure on 3CX Debian after LAN IP update

[Bits'n'Bytes]

Hi Everyone. I have a freshly minted Debian 3CX installed on an Intel NUC. Setup on my workbench, tested and working fine. Workbench subnet was 192.168.1.0/24. Picked up appliance and moved it to the clients network, subnet 192.168.0.0/24. Appliance picked up DHCP from clients network and 3CX interface accessible on NUC. However, DNS will not resolve on the Debian / appliance.

I have checked interfaces file and confirmed DHCP in place. Checked resolvers and confirmed IP of clients router was there. Also tried static IP and nameservers (local router, Google, etc) and nothing works. It is like DNS requests are being blocked, but the PC right next to on the same network is fine.

I am considering a complete rebuild, but if anyone has a suggestion as to what is going on and it can be fixed more simply it would be much appreciated.

 

[Saqqara]

Have you checked the resolv.conf file

https://www.tecmint.com/set-permanent-dns-nameservers-in-ubuntu-debian/

 

[NickD_3CX]

I am considering a complete rebuild, but if anyone has a suggestion as to what is going on and it can be fixed more simply it would be much appreciated.

I'd suggest first checking what @Saqqara said as it's very possible.

If you don't want to bother though and go directly for a full rebuild, you could take a 3CX Backup so you can at least keep any config you have made.
Then, reconfigure the whole system and instead of doing a clean install, just restore the backup.